1. Field of the Invention
The present invention relates to processes and apparatus for testing the sufficiency of lead bonds. More particularly, the invention relates to nondestructive test methods for TAB tape bonds to semiconductor chips.
2. Prior Art
Long term reliability of packaged semiconductor devices is dependent, among other things, on the integrity of the inner lead bond. Strength testing of lead bonds is based on the assumption that if the bond can withstand a minimum prescribed load, it is a joint that will not fail in normal use throughout the life of the product.
The inner lead bonding process on semiconductor devices has, in the past, been accomplished with wire bonding. This process has an inherent built in quality assurance opportunity in that as each wire is bonded, the bonding machine can give a slight controlled pull on the bonded wire thus assuring that the joint can at least withstand this predetermined force.
As device lead counts have increased and bonding densities have been increased, the industry has been moving towards tape automated bonding ("TAB") technology where the interconnecting wire is replaced with a prefabricated tape with the appropriate lead pattern formed on the tape. The leads have a generally rectangular cross-section and are bonded to the die by thermal compression.
The TAB process does not offer the built in bond process assurance of wire bonding since there is no way for the bonding machine to pull on the individual leads after the bonding step. Current test methods for TAB leads involve the manual utilization of a hook to pull representative samples of the bonded leads. This process is very slow and only permits random sampling to be conducted. Further, hook testing results destruction of the leads being tested.
It would be a significant advancement in the art to provide an apparatus and method for automatically testing TAB bonds. It would be an even further advancement if such apparatus and method provided for essentially 100% bond integrity verification and was nondestructive. The present invention provides an apparatus and method which achieve these advantages and others which will become more fully apparent from the following description and appended claims.